The present invention relates to a novel and useful apparatus for generating shortwave length radiation such as EUV and X-rays.
In the past, EUV and X-ray radiation has been created by contact between a laser beam and a metallic member such as one composed of phosphor bronze. For example, solid targets have been employed to generate shortwave electromagnetic radiation. Since the laser beam creating such radiation is pulsed, only a finite number of shots may be taken on a solid target, typically, 90,000 shots as an upper limit.
An alternate system of generating such shortwave electromagnetic radiation involves the use of a metallic tape composed of a similar material. For example, 500 meters of a bronze-phosphor tape will allow approximately 500,000 shots of a focused laser beam.
To successfully employ a tape target in such systems, the tape must be continually advanced across the laser beam focal point. It is most important that the tape remain in a plane during such advancement for maintaining the focus of the laser upon the tape, in order to produce an adequate supply of shortwave electromagnetic radiation. Although the focused laser beam creates shortwave electromagnetic radiation, the impingement of the laser beam on a tape composed of copper, phosphor-bronze, and the like, also creates dimples which extend from the tape on the side opposite to the side where the initial contact of the focused laser beam occurs. Such dimpling generates debris and, most importantly, creates an uneven surface. Such uneven surface when contacting a take-up spool or roller directs the moving tape outside of the focal plane of the laser beam and, thus, disrupts the focusing of the laser beam on the tape. Needless to say, such defocusing of the laser beam interrupts the production of shortwave radiation in a consistent and reliable fashion.
Many systems have been proposed to generate electromagnetic radiation by contact of a portion of a medium with an intense pulsed laser beam.
For example, reference is made to U.S. Pat. No. 5,038,155 which shows a recording apparatus having a heat sensitive sheet that is conveyed by a series of rollers into a recording apparatus section.
U.S. Pat. No. 5,759,336 describes a resist removing apparatus in which a tape unit is moved horizontally to apply adhesive tape in a strip to a wafer supported on an applicator table. Another wafer is placed over the first wafer and a table is moved to simultaneously apply adhesive tape to the second wafer and remove adhesive tape from the wafer on the table at the same time.
U.S. Pat. No. 6,238,515 includes a system for sticking a wafer to a ring frame by using a transfer tape. The transfer tape is stuck to both a ring frame and the back of the wafer to connect these two members. A protective tape peeling table interacts with the adhesive tape to complete the transfer of the wafer.
PCT Publication WO 01/37618 describes the method of producing extreme ultraviolet radiation utilizing a laser beam on a solid target where the emitted part of the radiation streams from the opposite surface of the target at its contact with a focused laser beam.
U.S. Pat. Nos. 5,003,543, 5,089,711, 5,151,928, and European Patent Application 0474011 describe laser X-ray sources in which a laser beam, amplified and focused, interacts with a plasma target. This target may take the form of a metal tape which is held in place by pinching guide rollers.
U.S. Pat. Nos. 5,539,764 and 6,538,257 show X-ray and extreme ultraviolet radiation sources in which a laser beam is focused on a tape that is run between two rollers contacting the same side of the tape.
U.S. Pat. No. 5,668,848 describes an X-ray target tape assemblage in which a pulse laser beam is focused on a tape to produce short wavelength radiation. The tape serving as the source of the short wavelength radiation is wound onto a drum obliquely in order to fully utilize entire width of the tape in this regard.
An apparatus which provides a source of shortwave electromagnetic radiation and overcomes the deficiencies of the prior art would be a notable advance in the field of radiation physics.